package Week4.J0508;

import java.util.Scanner;

public class 最长回文子序列_xv {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        char[] s = scanner.next().toCharArray();
        int n = s.length;

        int[][] dp = new int[n][n];

        for (int i = n - 1; i >= 0; i--) {
            dp[i][i] = 1;
            for (int j = i + 1; j < n; j++) {
                if (s[i] == s[j]) dp[i][j] = dp[i + 1][j - 1] + 2;
                else dp[i][j] = Math.max(dp[i + 1][j], dp[i][j - 1]);
            }
        }

        System.out.println(dp[0][n-1]);
    }
}
